New, more stringent emission limits for diesel engines necessitate the use of exhaust after-treatment devices. Emissions-related after-treatment strategies for vehicles have resulted in increased exhaust outlet temperatures, particularly during DPF/SCR “regeneration,” whereby accumulated particulate is cooked into ash, and undesirable combustion product gases are chemically converted to less undesirable gases through the injection of reactive fluids into their respective catalyst beds.
Exhaust systems without after-treatment devices typically discharge exhaust gas at a temperature of around 650 degrees Kelvin. During the regeneration cycle, the temperature of the exhaust gas plume may rise significantly above acceptable temperatures normally experienced by exhaust systems without such after-treatment devices. As an example, an exhaust system having an after-treatment device that includes a regeneration cycle may experience an exhaust gas plume temperature exceeding 900 degrees Kelvin at its center core. Exhaust gas at this high exit temperature creates a potentially hazardous operating environment. In the case of horizontal exhaust outlets, the hot exhaust comes in close proximity to ground level combustibles, such as grass or paper. For certain exhaust configurations, the high temperature gases can also present a safety hazard for people in proximity to the exhaust outlets.
Prior art and current exhaust pipe diffusers are not designed to optimally intermingle cooling air with a hot stream of exhaust gases, as described above. The result at the exit plane of the exhaust pipe can be a cool ring of exhaust flow surrounding a very hot exhaust core.
Thus, there exists a need for a flow diffuser for an exhaust pipe for diffusing hot exhaust gas on exit from an exhaust pipe